Imaging process employing charged donor and receiver sheets

ABSTRACT

AN IMAGING SYSTEM WHEREIN AN ELECTRICALLY PHOTOSENSITIVE IMAGING LAYER IS SUBJECTED TO AN INITIALLY HIGH ELECTRICAL FIELD AND WHILE UNDER SAID FIELD EXPOSED TO ELECTROMAGNETIC RADIATION TO WHICH IT IS SENSITIVE. SUBSEQUENT TO SAID EXPOSURE, THE ELECTRICAL FIELD IS REDUCED AND AFTER SUCH REDUCTION THE IMAGING LAYER IS RENDERED COHESIVELY WEAK, SANDWICHED BETWEEN A DONOR SHEET AND A RECEIVER SHEET AND WITH A FURTHER REDUCED ELECTRICAL FIELD PLACED ACROSS THE   DONOR AND RECEIVER SHEETS THE TWO SHEETS ARE SEPARATED. UPON SEPARATION OF THE SHEETS, THE IMAGING LAYER FRACTURES IN IMAGEWISE CONFIGURATION PROVIDING A POSITIVE IMAGE ON ONE OF THE SHEETS AND A NEGATIVE IMAGE ON THE OTHER.

Sept. 25, 1973 E. L. MENZ IMAGING PROCESS EMPLOYING CHARGED DONOR AND RECEIVER SHEETS Filed Jan. 6, 1971 N at ig INVENTOR. ELS l E LME NZ BY ATTORNEY United States Patent 3,761,258 IMAGING PROCESS EMPLOYING CHARGED DONOR AND RECEIVER SHEETS Elsie L. Menz, Rochester, N.Y., assignor to Xerox Corporation, Stamford, Conn. Filed Jan. 6, 1971, Ser. No. 104,329 Int. Cl. G03g 13/14, 13/22 U.S. Cl. 96-1 R 17 Claims ABSTRACT OF THE DISCLOSURE An imaging system wherein an electrically photosensitive imaging layer is subjected to an initially high electrical field and while under said field exposed to electromagnetic radiation to which it is sensitive. Subsequent to said exposure, the electrical field is reduced and after such reduction the imaging layer is rendered cohesively weak, sandwiched between a donor sheet and a receiver sheet and with a further reduced electric field placed across the donor and receiver sheets the two sheets are separated. Upon separation of the sheets, the imaging layer fractures in imagewise configuration providing a positive image on one of the sheets and a negative image on the other.

BACKGROUND OF THE INVENTION The present invention relates in general to imaging and more specifically to a system for the formation of images by layer transfer in image configuration.

Various imaging processes are known wherein a thin film of material is deposited on a substrate or image bearing surface to provide a contrast to said surface in image configuration. Due to the process steps employed, materials employed and defects therein, there is sometimes formed on the image bearing substrate unwanted imaging material in non-image or background areas of the image bearing substrate. Such unwanted image material is typically termed background material and is desirably eliminated by the use of optimum conditions and materials but many times even though such optimum conditions and materials are employed background material is found on the image bearing substrate after image formation. Imaging processes involving layer tranfser are subject to the problem of producing background material.

One such imaging process which provides images by means of layer transfer is described in copending application Ser. No. 708,380 filed Feb. 26, 1968, now U.S. Pat. No. 3,707,368. In this imaging system an imaging layer is prepared by coating a layer of electrically photosensitive imaging material onto a substrate. -In one form the imaging layer comprises a photosensitive material such as metal-free phthalocyanine dispersed in a cohesively weak insulating or semi-conductive binder. This coated substrate is called a donor. In some instances the imaging layer is not initially cohesively weak but is rendered cohesively weak by a process termed activation and in most cases it is desired that the imaging layer be activated during the imaging process to allow the shipping and storage of durable or cohesively strong imaging layers. Thus, in the imaging process described by the above mentioned copending application, generally termed manifold imaging, the process step of weakening the imaging layer involves contacting the layer with a swelling agent, softening agent, solvent or partial solvent for the imaging layer to weaken it to the extent required in order for it to fracture in the manifold imaging process. A receiver sheet is laid over the surface of the weakened imaging layer and an electric field applied across the imaging layer while it is exposed to a pattern of light and shadow representative of the image to be reproduced. Upon separation of the donor substrate and receiver sheet, the imaging layer fractures along the lines defined by the pattern of light and shadow to which the imaging layer has been exposed. Part of the imaging layer is transferred to one of the sheets While the remainder is retained on the other sheet so that a positive image, that is, a duplicate of the original is produced on one sheet while a negative image, in the photographic sense, is produced on the other.

As mentioned above, due to imperfections in materials or imaging conditions, there is sometimes adhering to the donor and receiver sheets portions of the imaging layer which are not part of the image and are in the background areas. Such materials are unwanted as they detract from the appearance and usefulness of the image thus produced. Although optimum conditions and imaging materials are strived for, in some instances the process must be operated so as to produce in addition to the image the unwanted background material. There is, therefore, a need for a simple and efiicient means of avoiding or significantly reducing the amount of background material produced together with the images by means of the imaging process.

SUMMARY OF THE INVENTION It is, accordingly, an object of this invention to provide an imaging system which overcomes the above noted disadvantages.

It is another object of this invention to provide a layer transfer imaging system which provides relatively high quality positive images on opaque materials.

It is another object of this invention to provide a system for layer transfer imaging which provides relatively high quality positive images on the receiver sheet.

Another object of this invention is to provide a manifold imaging process which produces images with significantly reduced or no background material.

These and other objects of this invention are apparent from the following description of the invention.

The above objects and others are accomplished in accordance with this invention by an imaging system utilizing a structure comprising an electrically photosensitive imaging layer coated on a donor sheet, hereinafter collectively referred to as a donor. In operation an electric field is placed across the imaging layer and the imaging layer is exposed to light projected from an image to be reproduced. After imagewise exposure, the electric field across the imaging layer is modified by reducing the electric field to a certain minimal value which will be more fully defined herein below. After the reduction in the electric field, the imaging layer is rendered cohesively weak or, in other Words, rendered structurally fracturable in response to the combined effects of an electric field which is less than the elecrical breakdown potential of the manifold set and exposure to electromagnetic radiation to which the imaging layer is sensitive. After being rendered cohesively weak, the imaging layer is contacted with a receiver sheet and with an electric field established across the thus formed manifold set at a further reduced level of strength the donor and receiver sheets are separated whereby the imaging layer fractures providing a positive image on one of the donor and receiver sheets and a negative image on the other.

Although it has been known previously in manifold imaging that modification of the electric field subsequent to exposure provides unique results such as the reversal of the photographic image sense on the respective sheets, such processes were performed upon electrically photosensitive imaging layers which were cohesively weak during the field modification. It has now been discovered that when the field modification takes place while the imaging layer is cohesively strong, or prior to its being rendered cohesively weak, the beneficial results are achieved particularly in the reduction of background material.

The extent to which the initial electric potential across the imaging layer is reduced prior to rendering the layer cohesively weak varies greatly and is dependent upon the original potential across the manifold set. The reduced potential is in the range from about /3 to about /2 or below the original potential at which the imaging layer is exposed.

Thus by modifying the sequence of the steps performed in the manifold imaging process, improved images are obtained. The materials employed in the process of this invention with respect to the donor substrate, receiver sheet, electrically photosensitive materials and binder materials employed together with the electrically photosensitive materials in the imaging layer are those employed in the prior art manifold imaging processes. Numerous examples of each of these materials are described in above mentioned copending application Ser. No. 708,380 which application is hereby incorporated by the reference.

The basic physical property desired in the imaging layer in order to form an image in accordance with the process of this invention is that it be frangible or structurally fracturable after having been suitably activated. That is, the layer must be sufficiently weak structurally so that the application of electrical field combined with the action of actinic radiation on the electrically photosensitive material will fracture the imaging layer. Further, the layer must respond to the application of field, the strength of which is below that field strength which will cause electrical breakdown or arcing across the imaging layer. Another term for cohesively weak, therefore, would be field fracturable.

As stated above, during the initial steps of the process of this invention the imaging layer is not structurally fracturable and is not so rendered until after having been subjected to the initial electrical field and exposure to the electromagnetic radiation to which it is sensitive. Only after the reduction of the potential thereby reducing the electrical field, is the imaging layer treated so as to reduce its cohesive strength to allow imagewise fracture. The activation step may take many forms which usually involves applying a substance to the surface of the imaging layer or including a substance in the imaging layer which substance lowers the cohesive strength of the layer or aids in lowering the cohesive strength. The substance so employed is termed an activator. Preferably, the activator should have a high resistivity so as to prevent electrical breakdown of the manifold sandwich. Accordingly, it will generally be found to be desirable to purify commercial grades of activators so as to remove impurities which might impart a higher level of conductivity. This may be accomplished by running the fluids through a clay column or by employing any other suitable purification technique. Generally speaking, the activator may consist of any suitable material having the aforementioned properties. For purposes of this specification and the appended claims, the term activator shall be understood to include not only materials which are conventionally termed solvents but also those which are partial solvent, swelling agents or softening agents for the imaging layer.

It is generally preferable that the activator have a relatively low boiling point so that fixing of the resulting image can be accomplished upon evaporation of the activator. If desired, fixing of the image can be accomplished more quickly with mild heating at most. It is to be understood, however, that the invention is not limited to the use of these relatively volatile activators. In fact, very high boiling point non-volatile activators including silicone oils such as dimethyl-polysiloxanes and very high boiling point long chain aliphatic hydrocarbon oils ordinarily used as transformer oils such as Wemco-C transformer oil, available from Westinghouse Electric Co., have also been successfully utilized in the imaging process. Although these less volatile activators do not dry off by evaporation, image fixing can be accomplished contacting the final image with an absorbent sheet such as paper which absorbs the activator fluid. In short, any suitable volatile or non-volatile activator may be employed. Typical activators include Sohio Odorless Solvent 3440, an aliphatic (kerosene) hydrocarbon fraction, available from Standard Oil Co. of Ohio, carbon tetrachloride, petroleum ether, Freon 214 (tetrafiuorotetrachloropropane), other halogenated hydrocarbons such as chloroform, methylene chloride, trichloroethylene, perchloroethylene, chlorobenzene, trichloromonofiuoromethane, trichlorotrifiuoroethane, ethers such as diethyl ether, diisopropyl ether, dioxane, tetrahydrofuran, ethyleneglycol monoethyl ether, aromatic and aliphatic hydrocarbons such vas benzene, toluene, xylene, hexane, cyclohexane, gasoline, mineral spirits and white mineral oil, vegetable oils such as coconut oil, babussu oil, palm oil, olive oil, =castor oil, peanut oil and neatsfoot oil, decane dodecanc and mixtures thereof. Sohio Odorless Solvent 3440 is preferred because it is odorless, nontoxic and has a relatively high flash point.

In addition, thermosolvents can be employed in the manifold set as described in copending application Ser. No. 628,028 filed Apr. 3, 1967, now US. Pat. No. 3,598,- 581 which application is incorporated herein by reference. When employing thermosolvents, the manifold set is heated to melt the thermosolvent under the reduced electrical field and while the imaging layer is in contact with the receiver sheet.

Whether the positive image is formed on the receiver sheet or donor sheet, depends on the imaging layer materials used and the initial polarity of the applied field. It has been found in general, however, if the donor side electrode is held at a positive potential with respect to the receiver side electrode that the positive image is formed on the receiver sheet and the negative image is formed on the donor sheet. That is, the illuminated portions of the imaging layer adhere to the donor sheet and the non-illuminated areas of the imaging layer adhere to the receiving sheet.

As stated above, according to the process of this invention, the imaging layer is subjected to an electrical field. The electrical field can be applied in many ways. Generally the sandwich is placed between electrodes having different electrical potential. Also, an electrical charge can be imposed upon one or both of the donor sheet and receiver sheet before or after forming the sandwich by any one of several known methods for inducing a static electrical charge into a material. Static charges can be imposed by contacting the sheet or substrate with an electrically charged electrode. Alternatively, one or both sheets may be charged using corona discharge devices such as those described in US. Pats. No. 2,588,699 to Carlson, US. Pat. No. 2,777,957 to Walkup, US. Pat. No. 2,885,556 to Gundlach or by using conductive rollers as described in US. Pat. No. 2,980,834 to Tregay et al., or by frictional means as described in US. Pat. No. 2,297,691 to Carlson or other suitable apparatus.

Thus, the electrical field can be provided by means known to the art for subjecting an area to an electrical field. The electrodes employed may comprise any suitable conductive material and may be flexible or rigid. Typical conductive materials include: metals such as aluminum, brass, steel, copper, nickel, zinc, etc., metallic coatings on plastic substrates, rubber rendered conductive by the inclusion of a suitable material therein, or paper rendered conductive by the inclusion of a suitable material therein or through conditioning in a humid atmosphere to insure the presence therein of suflicient water content to'render the material conductive. Conductive rubber is preferred because of its flexibility. In the process of this invention wherein the imaging layer is exposed to activating electromagnetic radiation while positioned between electrodes, one of the electrodes must be at least partially transparent. The transparent conductive electrode may be made of any suitable conductive transparent material and may be flexible or rigid. Typical conductive transparent materials include cellophane, conductively coated glass, such as tin or indium oxide coated glass, aluminum coated glass or similar coatings on plastic substrates. NESA, a tin oxide coated glass available from Pittsburgh Plate Glass Co., is preferred because it is a goodconductor and is highly transparent and is readily available. In the process of this invention wherein the donor and/or receiver is composed of conductive material each may also be employed as the electrodes by which the imaging layer is subjected to an electrical field. That is either when employed as an electrode one or both of the donor sheet and receiver sheet may serve a dual function in the process of this invention.

The strength of the electrical potential applied across the manifold set depends on the structure of the manifold sandwich and the materials used. For example, if highly insulating receiver and donor substrate materials are used, a much higher potential may be applied than if relatively conductive donor and receiver sheets are used. The potential required may, however, be easily determined. If too large a potential is applied, electrical breakdown of the manifold sandwich will occur allowing arcing between the electrodes. If too little potential is applied, the imaging layer will not fracture in imagewise configuration. By way of example, if a 3 mil Mylar receiver sheet and a 2 mil Mylar donor sheet are used, potentials as high as 20,000 volts may be applied between the electrodes. The preferred potential across the manifold sandwich are, however, in the range of from about 2,000 volts per mil to about 7,000 volts per mil of electrically insulating material. Since relatively high potentials are utilized, it is desirable to insert a resistor in the circuit to limit the flow of current. Resistors on the order of from about 1 megohm to about 20,000 megohms are conventionally used.

As stated above the initial electrical field is reduced in accordance with the process of this invention prior to rendering the imaging layer structurally fracturable. Also, as stated above, the reduction in electrical field depends in large measure on the inital field employed and one skilled in the art guided by the above disclosure can easily determine the extent to which the electrical field is to be reduced in accordance with the process of this invention.

It has also been found that certain imaging layers respond to the process of this invention without exposure to activating electromagnetic radiation. By charging the set by applying a field across the layer and then modifying the field across the layer in accordance with the process of this invention, certain imaging layers are found to fracture in imagewise configuration. It is, therefore, possible to provide a system wherein the manifold set is given a uniform charge and then placed in an imagewise field of reduced potential. After being subjected to the imagewise field, the imaging layer is activated or suitably weakened. Upon separation of the donor and receiver sheets, the imaging layer fractures in imagewise configuration providing a positive image on one of the sheets and a negative image on the other. For these imaging layers then, it is not necessary to provide photosensitive pigments dispersed in a binder, instead, pigments not considered photosensitive may be incorporated in the imaging layer. Typical of these pigments are carbon black, iron oxides, lead chromate in paste form designated alkyd paste, titanium dioxide, lead chromate and the various pigments used in printing inks and mixtures thereof.

The process of this invention may take many forms. For example, the snadwich of donor sheet, imaging layer and receiver sheet can be drawn between two wire electrodes which are connected to a source of potential difference. A charge is thereby placed on both surfaces of the electrically insulating material. Alternatively, either or both of the receiver sheet or donor sheet can be charged before being brought together in the manifold set. After charging, the imaging layer is then exposed to a pattern of light and shadow representative of the image to be reproduced. After exposure, the electric field is reduced as described above and the imaging layer is activated. The manifold set is reformed and the further reduced potential is placed across the manifold set. Upon separation of the manifold set with the further reduced potential across the set, the imaging layer fractures in imagewise configuration.

The amount of further reduction of the potential from the point at which activation occurs again varies depending upon the materials employed and the initial potential applied. Generally, a reduction in the range of from about /2. to about /2 or below the potential at which activation occurred will provide satisfactory development of the image.

Alternatively, the imaging layer may be exposed to electromagnetic radiation to which it is sensitive either before or after sandwich formation providing it is subjected to the initial higher electric field during exposure. If the imaging step is performed after sandwich formation, then at least one of the donor and receiver sheets must be transparent to the electromagnetic radiation employed. Various methods of electrostatically charging the donor sheet and imaging layer of the entire manifold set have been described above.

When employing electrostatically insulating donor sheet, the donor sheet usually retains electrostatic charges from the electric filed applied during imagewise exposure of the imaging layer followed by a reduction in the electric field. These charges can be employed to develop the image in a method wherein the manifold set is bounded on either side by conductive layers and the conductive layers are electrically interconnected. According to this method, the exposed imaging layer residing on an insulating donor sheet is removed from the electrode which supplied the initial and reduced field and laid upon a receiver sheet which in turn is backed by a conductive backing layer. A conductive layer is placed over the donor sheet and electrically interconnected with the conductive backing of the receiver sheet. With the two conductive layers so connected, the donor and receiver sheets are separated thereby fracturing the imaging layer providing a positive and a negative image.

When employing this method of developing the image, care must be taken to separate the donor from the receiver as soon as practical after electrically interconnecting the conductive layers. If a delay is caused, inferior images will result. Preferably, the separation occurs immediately after electrically interconnecting the conductive layers. However, if an applied potential, even of small value, is maintained on the donor sheet, the time delay in separating the manifold set in unimportant. That is, high quality images can be provided even though a time period elapses prior to the separation of the manifold set. The applied potential can be significantly below the potential to which the imaging layer is reduced prior to the activation step. For example, an applied potential of several hundred up to 1,000 volts applied to the donor will eliminate the need for a consideration of timing in the separation of the manifold set after activation.

In accordance with the process of this invention, background free images can be developed on a wide variety of image receiving media. For example, images can be developed on cloth, drafting film, vellum, ordinary paper, leather, thermoplastic materials, photographic film, metals such as iron, silver, aluminum, tin, etc. In addition, images can be developed in accordance with the process of this invention on irregular surfaces which would be unusable in the usual manifold process of the prior art. That is, in one or more of the process steps of the prior art by which the image is originally formed, smooth surfaces are required least incomplete processing occur on an irregular surface. However, as will be seen in the following examples, many different types of surfaces may be employed as the image receiving medium in the process of this invention. In addition, highly useful image receiving media can be employed such as metal or plastic lithographic plates. Surprisingly, high quality prints can be prepared from lithographic plates made from images developed in accordance with the process of this invention.

When employing flat plate electrodes adjacent the donor sheet to apply the electric field across the imaging layer during imagewise exposure, a particularly preferred embodiment of the process of this invention is one in which a liquid is employed between the donor substrate and the fiat plate electrode. It has been found that the use of a liquid, either electrically insulating or conduuctive, helps improve the quality of the image obtained by the process of this invention. A thin film of liquid between the donor sheet and the electrode eliminates the possibility of air pockets or voids due to unevenness of materials which in some instances have been found to deleteriously affect the quality of the image. Liquids such as water and kerosene fractions have been found useful for this purpose.

DESCRIPTION OF THE DRAWINGS The advantages of this improved method of imaging will become apparent upon consideration of the detailed disclosure of the invention especially when taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a side sectional view of a photosensitive imaging member for use in the invention.

FIG. 2 is a side sectional view diagrammatically illustrating the application and modification of electric field across the imaging layer together with the exposure of the imaging layer.

FIG. 3 is a side sectional view of the activation and image development steps of the process of this invention.

Referring now to FIG. 1, imaging layer 2 comprising photosensitive particles 4 dispersed in binder 3 is deposited on an insulating donor substrate or sheet 5. The image receiving portion of the manifold set comprises an insulating receiver sheet 6. Either or both of sheets 5 and 6 may be transparent so as to permit exposure of imaging layer 2. The embodiment of the invention shown in FIG. 1 is preferred because it allows for the use of inexpensive high-strength insulating material as donor and receiver sheets.

Referring now to FIG. 2, the first step illustrated is the step of subjecting the electrically photosensitive imaging layer 12 sandwiched between receiver sheet 14 and donor sheet 16 to an electrical field which is applied across the manifold set through electrodes 18 and 21 which are connected to potential source 28 and resistor 30. Drive rollers 26 direct the path of travel of the manifold set between electrodes 18 and 21 which although not shown to be touching can be charged rollers in virtual contact with the manifold set. The path of travel of the manifold set is then directed to transparent plate 27 where it is exposed to a light image 29. Light image 29 may be pro jected through a transparency or can be light information projected from an opaque substrate. In a continuous operation, the light image is preferably projected through a slit so that there is little or no relative movement between the projected image and the manifold set during exposure. Subsequent to exposure, the electric field across the manifold set is modified by electrodes 32 and 34 which are connected to power source 31 through resistor 33. Electrodes 32 and 34 are under a significantly lower potential than are electrodes 18 and 21 thus reducing the electric field across the imaging layer.

Referring now to FIG. 3, there is shown the activation step in the process of this invention. In the stage of the imaging process, the manifold set is open and the activator is supplied to imaging layer 12 or to receiver sheet 38 following which these layers are placed together. Although the activator may be applied by any suitable technique such as with a brush, with a smooth or rough surfaced roller, by How coating by vapor condensation or the like, FIG. 3 diagrammatically illustrates the activator fluid 39 sprayed onto imaging layer 12 of the manifold set from container 40. Following the deposition of the activator fluid, the set is closed by conductive rollers 42 which serve to squeeze out any excess activator fluid which may have deposited. Rollers 42 are also electrically interconnected by means of wire 44 and both rollers are grounded. Rollers 42 also act as a bearing point for the separation of the donor and receiver sheets. FIG. 3 shows receiver 38 being lifted from donor 16 thereby fracturing imaging layer 12 along the edges of the exposed areas and at the surface where it had adhered to donor 16. Accordingly, once separation is complete exposed portions of imaging layer 12 are retained on one of layers 38 and 16 while substantially unexposed portions are retained on the other layer.

Although FIG. 2 is intended to represent the use of thin roller electrodes 18, 21, 32 and 34, these electrodes may be conductive rods, brushes edges or conductive objects, strips of conductive material, wire or other suitable charging means. In addition, charging may be accomplished by the use of a corona discharge device on one or both surfaces of the manifold set.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples further specifically illustrate the present invention. The examples below are intended to illustrate various preferred embodiments of the improved imaging method in the invention and is not intended to be limited thereby. The parts and percentages given are by weight unless otherwise indicated.

EXAMPLE I An imaging layer comprising electrically photosensitive materials dispersed in a binder is first prepared. About parts of Naphthol Red B, code 20-7575 available from American Cyanamide Company is dissolved in reagent grade ethylenediamine. The solution is filtered immediately through coarse filter paper and the filtrate mixed with an equal volume of reagent grade isopropanol. The Naphthol Red B precipitates in the alcohol and is removed by means of a centrifuge. After separating the ethylenediamine and alcohol, the electrically photosensitive material is washed and filtered with successive amounts of isopropanol, a 2:1 volume mixture of isopropanol and deionized water and five washings with deionized water until the filtrate is neutral. Finally, the material is washed with dimethylformamide and methanol in succession until the filtrates have a pale yellow color. The Naphthol Red B is then dried at 40 C. under vacuum. About 3 parts of the purified Naphthol Red B is combined with about 45 parts of naphtha and ball milled for 4 hours.

A binder material is prepared by combining about 2.5 parts of Paraflint RG, a low molecular weight parafiinic material available from the Moore and Munger Co., New

York City; about 3 parts of Polyethylene DYLT available from Union Carbide Corporation; about .5 part of vinyl acetate-ethylene copolymer available as Elvax 420 from E. I. du Pont de Nemours Inc. and about 2.5 parts of a modified polystyrene available as Piccotex 100 from Pennsylvania Industrial Chemical Co. with about 15 parts of Sohio Odorless Solvent 3440, a kerosene fraction available from the Standard Oil Company. The mixture is heated until dissolved and then cooled. The binder and pigment mixture is then ball milled for a period of about 18 hours. About 45 parts of isopropyl alcohol are added to the mixture and the mixture is milled in the ball mill for 15 minutes. The resulting imaging material is then coated on 1 mil Mylar with a No. 18 wire wound drawdown rod to provide a coating weight of .16 gram per square foot to produce a donor. The donor i dried at a temperature of about 115 F.

The donor is then placed on the tin oxide surface of a NESA glass plate with the imaging layer facing away from the tin oxide. A sandwich is formed by placing a film of aluminized Mylar over the imaging layer with the aluminizegi surface facing the imaging layer as an electrode and a 5,000 volt DC. potential is applied across the sandwich between the NESA glass plate and the aluminized Mylar electrode. With the field applied, the imaging layer is exposed to a positive image pattern by an incandescent white light source of 12.5 ft. candles for a period of 3 seconds through the transparent donor. The potential is then reduced to 1200 volts and the sandwich is separated. The imaging layer remains intact on the donor sheet. A paper receiver is prepared by laying a sheet of bond paper on a conductive sheet and wetting the paper with Sohio Odorless Solvent 3440, a kerosene fraction, available from the Standard Oil Company. The donor is removed from the electrode and laid imaging layer side down on the wetted bond paper whereupon the imaging layer is activated by the flow of liquid on the paper. A conductive rubber sheet is laid over the donor and it is electrically interconnected with the conductive sheet under the bond paper. Immediately upon connecting the rubber conductor and the conductor under the bond paper, the donor sheet together with the rubber conductor is separated from the paper revealing a high quality positive image residing on the paper and a negative image residing on the donor.

EXAMPLE II A donor prepared as described in Example I is laid upon the tin oxide surface of a NESA glass electrode and a black paper electrode is laid over the imaging layer. The NESA electrode is connected to the positive pole of a DC. power supply and the black paper electrode is connected to the negative pole. The voltage between these electrodes is raised to 5,000 volts and while maintained at 5,000 volts the imaging layer is exposed through the NSEA glass and donor sheet as in Example I. The voltage is then reduced to 1200 volts and the black paper electrode is lifted from the imaging layer. The imaging layer is activatedby applying a small amount of Sohio Odorless Solvent to the layer by means of a brush and a 1 mil thick Mylar receiver sheet is laid over the activated imaging layer. The voltage on the NESA is set at 800 volts and the black p'aper electrode is placed over the receiver sheet. While maintaining 800 volts between the electrodes, the sandwich is separated. After a period of about 1 minute, a high quality positive image resides on the receiver sheet while a negative image resides on the donor sheet. This example illustrates the use of a small amount of potential under the donor sheet during the time the imaging layer is activated thereby perserving a high quality image on the receiver sheet.

EXAMPLE III A black imaging layer useful in the manifold imaging process is prepared by combining about 5 grams of x-form phthalocyanine with about 5 grams Algol Yellow GC, 1,2,5,6-di-(C)C-diphenyl thiazole-anthraquinone, 01. No. 67300, available from General Dyestuffs Corporation, and about 2.8 grams of purified Watchung Red B, 1-(4'-methyl-5-chloro-2'-sulfonic acid) azo-benzene-Z- hydroxy-3-naphthoic acid, C.I. No. 15865, available from E. I. du Pont de Nemours & Co., about 8 grams of Sunoco Microcrystalline Grade 5825 having an AST M melting point of 151 F., available from Sun Oil Company and about 2 grams Parafiint R'G, a low molecular weight paraifinic material available from the Moore & Munger Company, New York City and about 320 ml. of petroleum ether (l20 C.) and about 14 ml. of Sohio Odorless Solvent 3440 are placed with the mixed pigments in a glass jar containing /2 inch flint pebbles. The mixture is then milled by revolving the glass jar at about 70 r.p.m. for about 16 hours. The mixture is then heated for approximately 2 hours at about 45 C. and allowed to cool to room temperature. The paste-like mixture is then coated in subdued green light on 1 mil thick Mylar sheet by means of a #22 wire wound drawdown rod to produce a coating weight of about .27 grams per square foot.

The imaging layer on the Mylar is then dried at F. The dried donor is laid on the tin oxide surface of a NESA electrode and the aluminized surface of an aluminized sheet of 2 mil Mylar is placed over the imaging layer as an electrode. NESA glass and the aluminized surface are connected to the positive and negative poles of a DC. power supply respectively. The potential between the electrodes is raised to 4,000 volts and while maintained at that level the imaging layer is exposed to a pattern of light from an incandescent light source for a total exposure of .34 foot-candle seconds. Subsequent to exposure, the potential is reduced to 1,500 volts whereupon the aluminized Mylar is removed from the imaging layer. The donor together with the imaging layer still intact thereon is placed in contact with a metal litho plate which has been wetted with Sohio Odorless Solvent 3440. A conductive rubber sheet is placed over the donor and connected to the metal litho plate. Immediately, the donor and rubber sheet is removed from the metal plate leaving a dense background free black image on the litho plate while a negative image resides on the donor sheet.

EXAMPLE IV The procedure of Example I is repeated with the exception that a metal lithographic plate is employed in place of the bond paper. Upon separation of the donor from the lithographic plate, there is provided a positive image residing on the litho plate.

EXAMPLE V The procedure of Example I is repeated with the ex- I ception that exposure is for 2 seconds at 5.6 foot-candles to provide a total of 10.8 foot-candle seconds exposure. A voltmeter is placed in the connection between the conductive backing for the donor sheet and the metal plate under the bond paper. When the conductive backing and metal plate are connected, the voltmeter indicates an initial high voltage and then returns to zero when at zero voltage the donor is removed from the bond paper revealing an inferior positive image on the bond paper.

EXAMPLE VI The procedure of Example V is repeated with the exception that the donor sheet is removed from the paper at the maximum reading of voltage on the voltmeter. A superior quality positive image is found residing on the bond paper.

EXAMPLE VII The procedure of Example I is repeated with the exception that a small amount of water sufiicient to coat the surface of the NESA electrode is placed between the 11 electrode and the donor. Upon separation of the donor from the paper, an image superior in quality to that obtained in Example I is left residing on the paper.

EXAMPLE VIII The procedure of Example III is repeated with the exception that a small amount of Sohio Odorless Solvent 3440 sufficient to coat the NESA electrode is placed between the donor and the electrode. A positive image superior in quality to that obtained in Example III is produced.

EXAMPLE IX The procedure of Example I is repeated with the exception that the potential between the electrodes is raised to 7000 volts while the exposure is continued for a total incident exposure of 39 foot-candle seconds. The voltage is then lowered to 4000 volts and the imaging layer is activated. The image is then developed as in Example I.

EXAMPLE X The donor of Example I is placed on a tin oxide surface of a NESA glass electrode and a black paper electrode placed over the imaging layer. The electrodes are connected to a 8000 volt DC. power supply with the NESA connected to the positive pole. After raising the potential across the imaging layer to 8000 volts, the black paper electrode is removed and the imaging layer is exposed from its exposed surface to an image pattern of white incandescent light for a total incident exposure of about 28 foot-candle seconds. The black paper electrode is then replaced on the imaging layer, the potential is reduced to 3,000 volts and the black paper electrode is again removed. The donor with the imaging layer thereon is then removed from the NESA electrode and an image is developed in accordance with the procedure of Example I. Removal of the donor from the wetted paper, a positive image is found residing on the paper.

Although specific components and proportions have been stated in the above description of preferred embodiments of the invention, other typical materials as listed above as suitable may be used with similar results. In addition, other materials may be added to the various components of the process to synergize, enhance or otherwise modify the properties of the imaging layer. For ex ample, various dyes, spectral sensitizers, activators or electrical sensitizers such as Lewis acids may be added to the several components of the manifold sandwich.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An imaging process which comprises the steps of:

(a) subjecting an electrically photosensitive imaging layer to a first electric field and exposing said layer to electromagnetic radiation to which it is sensitive;

(b) reducing the potential of the electric field across said imaging layer at least about /2 of the original value;

(c) subsequent to said exposure and reduction of field,

activating said imaging layer to render it structurally fracturable in response to the combined effects of an electric field and exposure to electromagnetic radiation to which it is sensitive by contacting said layer with an activating amount of an activator;

(d) sandwiching said activated layer between a donor sheet and a receiver sheet and extending a further reduced potential across said sandwich; and

(e) separating said sandwich whereby said imaging layer fractures in imagewise configuration providing a positive image on one of the donor and receiver sheets and a negative image on the other.

2. The process of claim 1 wherein the electrically photosensitive imaging layer comprises an organic electrically photosensitive material.

3. The process of claim 2 wherein the organic electrically photosensitive material is dispersed in an insulating binder.

4. The process of claim 1 wherein the activator is selected from the group consisting of solvents, partial -solvents, swelling agents and softening agents for said imaging layer.

5. The process of claim 1 wherein the electric potential is reduced to a range of from about /2 to about /3 of its original value.

6. The process of claim 1. wherein the donor sheet is electrically insulating and retains a static electric charge from the reduced field and said static electric charges are utilized to place an electric field across said sandwich by placing electrically interconnected conductive layers on each side of said sandwich.

7. The process of claim 6 wherein said receiver sheet is electrically conductive.

8. The process of claim 1 wherein a liquid resides between said donor and the electrodes employed to establish said potential across the imaging layer and to reduce said potential.

9. The process of claim 1 wherein an applied potential of lower value than said reduced potential is employed across the imaging layer during said sandwich separation.

10. The process of claim 1 wherein the electrically photosensitive imaging layer comprises a mixture of electrically photosensitive materials dispersed in an electrically insulating binder.

11. An imaging process which comprises the steps of:

(a) subjecting an imaging layer to a first electric field;

('b) reducing the electric field in imagewise configuration;

(c) subsequent to said reduction of field, activating said imaging layer to render it structurally fracturable in response to the effect of an electric field;

(d) sandwiching said imaging layer betwen a donor sheet and a receiver sheet and placing a further reduced electric field across said sandwich; and

(e) separating said sandwich whereby said imaging layer fractures in imagewise configuration.

12. The process of claim 1 wherein the electric field of step (a) is in the range of from about 2000 volts per mil to about 7000 volts per mil.

13. The process of claim 11 wherein the electric field of step (a) is in the range of from about 2000 volts per mil to about 7000 volts per mil.

14.. An imaging process which comprises the steps of:

(a) subjecting an electrically photosensitive imaging layer to a first electric field and exposing said layer to electromagnetic radiation to which it is sensitive while said layer is sandwiched between donor and receiver sheets, at least one of said sheets being at least partially transparent to electromagnetic radiation to which said layer is sensitive;

(b) reducing the potential of the electric field across said sandwich;

(c) subsequent to said exposure and reduction of field, rendering said imaging layer structurally fracturable in response to the combined effects of an electric field and exposure to electromagnetic radiation to which it is sensitive by contacting said layer with an activating amount of an activator;

(d) placing electrically interconnected conductive layers on each of said donor and receiver layers and;

(e) separating said donor sheet from said receiver sheet while each is in contact with said conductive layer whereby said imaging layer fractures in imagewise configuration providing a positive image on one of the donor and receiver sheets and a negative image on the other sheet.

15. The process of claim 14 wherein the electric field of step (a) is in a range from about 2000 volts per mil to about 7000 volts per mil and the electrical potential is reduced to a value in the range of from about /2 to about /3 of its original value.

16. The method of claim 15 wherein a liquid resides between the donor and the electrode employed to establish said potential across the imaging layer.

17. The process of claim 14 wherein the electrically photosensitive imaging layer comprises an organic electrically photosensitive material dispersed in an insulating binder.

14 References Cited UNITED STATES PATENTS 3,565,612 2/1971 Clark 961 3,573,904 4/1971 Clark 961 GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner U.S. Cl. X.R. 

